The invention relates to a process and apparatus for producing bristle articles, comprising a bristle carrier of a mouldable or foamable material and plastic bristles anchored therein, with the bristles, in the form of single bristles or bristle strands, being inserted through channels and sleeves extending the same into a mould for the bristle carrier and being thermally melted at the end thereof located in the mould for forming a thickened portion, which is then sealingly engaged at the opening of the sleeve projecting into the mould, and with the mould being subsequently filled with the bristle carrier material.
Since the appearance of plastics, numerous attempts have been made to utilize the thermoplastic behavior of plastics for producing the connection or joint between bristles and bristle carriers. Thus, it was proposed in, for example (German Patent 355 645), to introduce the fixing ends of the bristles into a mould for the bristle carrier and to fill the cavity with a thermally plasticizable material.
This process was modified in, for example, (German Patent 895 140 in such a way that the same materials were used for the bristles and bristle carrier, namely polyamides or polyurethanes, so that at the elevated processing temperature a type of thermal fusion occurs between the two materials. However, this only makes it possible to produce bristle articles with the materialspecific characteristics of the particular material used and which are only able to meet specific use requirements. In addition, the specifically proposed materials are relatively high-grade plastics, which would lead to an unacceptable price increase for many bristle articles.
Nowadays bristle carriers are generally produced by a foaming or injection moulding process, which therefore immediately suggests itself for performing the aforementioned process. However, in injection moulding problems have occurred, because the liquid material injected into the mould penetrates between the bristle and between the bristles and the channels guiding them so that, after hardening, there is an undesired, irregular bristle-side sealing face on the bristle carrier. In the vicinity of its attachment to the bristle carrier, the bristle bundle also looses its elasticity and, as the penetration does not take place uniformly, in certain circumstances the different bristle bundles can have different bending characteristics. It is either impossible or only possible with great effort and expenditure to subsequently clean the attachment points.
Therefore numerous attempts have been made such as, for example, in DE-OS 29 22 877, to seal the guide channel for each bristle bundle, in that e.g. the injection moulding material is initially injected with limited pressure and prehardened on one mould wall and only then is the larger quantity of injection moulding material introduced into the mould. This process is extremely complicated if it is wished to obtain a completely satisfactory sealing face on the bristle carrier. In addition, for assisting rapid solidification of the material in the bristle attachment area, an intense cooling of the channels have been produced, which is impossible when the bristle bundles are closely juxtaposed. The proposal to produce a counterpressure to the injection moulding pressure in the guide channels is also not practicable, because this counterpressure leads to an irregular sealing face on the bristle carrier. The same applies with respect to the sealing of the openings of the guide channels prior to the injection moulding process and which are then opened after the pressure reduction in the mould and subsequently the bristle strands are then pressed into the still soft plastic material. This also impairs adhesion between the bristles and the bristle carrier material. The problem is also not solved by mechanical seals in the vicinity of the guide channels, e.g. as a result of a conical constriction of the opening or sealing lips located at this point, because it is not possible to pack the bristles sufficiently tightly together to ensure that no capillary spaces are left between them.
To improve the binding of the bristles into the bristle carrier, it is also Proposed in, for example, German Patent 845 933, French Patent 1 453 829 and U.S. Pat. Nos. 2 643 158 and 2 655 409, to melt and optionally deform the bristle ends extending into the cavity, so that the end of each bristle bundle is provided with a thickened portion exceeding its diameter and which is positioned at a distance from one mould wall. After injecting or foaming around the bristle end, the latter are positively and non-positively anchored in the bristle carrier, so that an adequate extraction resistance is obtained However, this does not solve the problem of the bristle carrier material appearing in the guide channels of the bristle strands and between the bristles.
A number of proposals such as described, for example, in EP-OS 142 885, EP-OS 149 996 and German Patent 35 11 528, deal with the special problem of producing the thickened portion and sealing the bristles or bristle bundles in the guide channels of the mould with respect to the bristle carrier material injected into the same. Thus, in one (EP-OS 142 885 the bristle bundles are introduced into the guide channels of a holding plate and are melted at the ends projecting above the same to give thickened portions. The holding plate with the thickened portions projecting over the same is then brought to the open side of an injection mould until the latter is tightly sealed and the bristle carrier material is then injected into the mould. Under the action of the injection moulding pressure, the thickened portions are supposed to sealingly engage with the openings of the guide channels, so as to prevent the penetration of bristle carrier material between the bristles on the one hand and between the bristles and the wall of the guide channels on the other. However, this proposal is not successful in practice. The injection moulding pressure builds up virtually isostatically in the mould, so that it also migrates behind the thickened portions and leads to the opposite to what is desired. Namely, the bristle bundles are drawn into the mould and the bristle carrier material penetrates between the bristles in the guide channels.
In a further process described in EP-OS 149,996 the bristle ends are melted outside the mould, subsequently introduced into the latter through the guide channels at high speed and initially compressed against a plate, so as to give a thickening to the still plastic bristle ends. The exertion of pressure on the thickened portions is intended to sealingly engage them against the guide channel openings and subsequently the bristle carrier material is injected. However, this process is also unusable in practice, because without technical aids acting directly on the thickened portion, a sufficiently high contact pressure on the openings is not possible.
Better results can be obtained with a process described for example, in German Patent 35 11 528, if the bristles projecting through the guide channles into the mould are melted at their ends and the resulting thickened portion is brought up to the guide channel opening under tension on the bristles. This process requires no measures within the mould cavity for producing the necessary sealing forces, the latter being applied from outside the mould and precisely with the order of magnitude necessary for a satisfactory seal. A particularly favourable process variant provides for the displaceable mounting of a sleeve within the guide channel and which is used for guiding the bristle strands or bundles. This guide sleeve initially projects into the mould cavity and the bristle ends project over its opening. The bristle ends are melted and shaped onto the guide sleeve opening, accompanied by the formation of a thickened portion. The sleeve is subsequently retracted into the guide channel and the thickened portion is sealingly drawn against its opening or the guide channel opening.
In the three latter cases the anchoring of the bristles within the bristle carrier takes place in that an undercut is formed between the thickened portion in the mould cavity and the mould wall having the guide channels and the bristle carrier material flows into said undercut. Thus, the bristles are anchored directly below the bristle carrier surface and, consequently, have little or only an inadequate guidance within the bristle carrier material. In addition, the bristle carrier material flowing into the undercut only has a very limited thickness, so that it can only absorb limited extraction forces acting on the bristles. Finally, the quality of the anchoring is largely dependent on the extent to which the undercut or a specific size thereof can be guaranteed. In view of the plastic deformation, this is only possible to a very limited extent.